The present invention relates to a method of producing moulded pulp articles by deposition of fibres on a respective suction mould such that the moulded pulp articles have a high content of dry matter when leaving the suction wheel and to an apparatus for carrying out the method. In this connection the term xe2x80x9cpulpxe2x80x9d is to be understood as applying to a fibre containing pulp mass, that may also contain or constitute of waste paper.
Document U.S. Pat. No. 3,654,076 discloses a method of continuous mass production of articles from pulp material using a moulding machine with a rotatable mould carrier, on the periphery of which suction moulds are placed side by side. The moulded pulp articles are formed by immersing the suction moulds into a vat of suspended pulp material while suction is applied in order to form a body of pulp in the shape of the desired article by fibre deposition. The suction mould is then withdrawn from the vat of suspended pulp material, and the suction is generally continued to compact the deposited fibres while exhausting residual liquid therefrom. The moist moulded articles are removed from the suction mould, partly by blowing air through the suction mould, and partly by aspirating the articles onto a corresponding transfer rotor. From the transfer rotor, the articles are placed onto supporting and conveying means adapted to convey the articles to a drying oven for a drying process. The moulded articles have, when leaving the suction mould, a relatively low dry matter content, which is typically about 25 weight %. A dry matter content of about at least 90 weight % has to be achieved by drying the articles in a drying oven. The low initial dry content of the articles when leaving the suction mould results in a high amount of energy used for drying the articles in the oven. Moreover, the articles with their low dry content are difficult to handle due to their low form stability, i.e. they need to be handled carefully.
U.S. Pat. No. 4,448,640 discloses a method of continuous mass production of articles from pulp material using a moulding machine with a rotatable mould carrier according to the above described principles which is provided with a stationary hood that roughly encapsulates a part of the rotatable mould carrier. This arrangement allows to flow a mixture of hot air or humid hot air and ambient air through the articles on the suction moulds.
On the above background it is the object of the present invention to provide a method of the kind referred to initially, with which it is possible to produce articles with a high dry matter content when leaving the suction mould. The advantages of a high dry content are a better form stability resulting in easier handling of the articles in following production steps, such as e.g. after-pressing and a reduction in the energy needed to dry the articles. This object is achieved with the method by delivering a de-watering fluid to a substantially hermetically sealed space over the article, whereby it is possible to flow de-watering fluid through the article which is not mixed with ambient air and thus achieve a substantially improved de-watering effect leading to a higher dry matter content of the moulded pulp articles.
The present invention also relates to an apparatus to carry out the above-mentioned method. By providing a hood over the suction moulds or the mould carrier in combination with gaskets sealing between the moulds and the hood or hoods, a space over the article can be efficiently sealed from the ambient air. By delivering a de-watering fluid to the encapsulated space over the mould surface, only the de-watering fluid is flowed by suction through the moulded pulp articles on the mould without ambient air being mixed into the de-watering fluid.
It is a further object of the invention to provide a method of the kind referred to initially in which steam is used as a de-watering fluid.